The present invention concerns an intervertebral disc prosthesis, intended to be substituted for fibro-cartilaginous discs ensuring connection between the vertebrae of the spinal column.
Various types of intervertebral disc prostheses are known in the prior art. Numerous prostheses, such as for example in the patent applications WO 02 089 701 and WO 2004/041129, are constituted by a lower plate and an upper plate forming a sort of cage articulated about a central core. Other prostheses such as those described in the U.S. Pat. No. 5,676,701 and in the patent application WO 03/059212 A1, for example, comprise only a lower plate and an upper plate articulated to one another by means of an articulation surface. The advantage of these two types of articulated prostheses is that they offer freedom of movement for the patient wearing the prosthesis, by enabling inclination and/or rotation of one of the plates relative to the other. The additional advantage of prostheses comprising a central core, mobile between the plates, is that they allow spontaneous positioning of the core in the ideal position to absorb the constraints imposed on the prosthesis. Some of the prostheses whereof the central core is mobile between the plates comprise cooperation means present on the core and on at least one of the plates to limit displacement of the core. In these prostheses described in the prior art, osseous anchoring means are likewise known which fix each of the plates of the prosthesis in each of the vertebrae between which the prosthesis is intended to be implanted. These osseous anchoring means can consist of fins intended to be fixed on the plates of the prosthesis and cooperate with a groove made in the surface of the vertebral plates or in anchors intended to be planted in the vertebral body.
However, the disadvantage of these prostheses is that they are not easy to insert between the vertebrae, since implantation requires good stability of the different elements of the prosthesis between one another. This stability is often missing in prostheses known from the prior art and the known instrumentation does not generally ensure stability of the elements of the prosthesis. In fact, the articulated plates of the prostheses possess degrees of liberty conferring comfort to the patient, but discomfort for the surgeon who fits them. The plates risk inclining and turning about their articulation surfaces. The surgeon is therefore not guaranteed that the elements are properly aligned in the antero-posterior axis of the vertebral column.